Bingxu (丙戌) Dinghai (丁亥) Wushangtu (屋上土) refers to the element of fire associated with Bing (丙) and Ding (丁), while Xu (戌) and Hai (亥) are considered the heavenly gates. Since fire naturally rises, the earth is not born below but above, hence it is called Wushangtu (屋上土), meaning "Earth on the Roof."